Automotive cooling systems typically include one or more heat transferring fluid systems to maintain an internal combustion engine operating within a desired temperature range, thereby increasing efficiency. Many automotive cooling systems include a solution of antifreeze in water. The solution is pumped in a closed circuit that includes cooling jackets around the combustion chambers of the internal combustion engine where thermal energy is absorbed by the solution. The solution is then passed through a heat exchanger (radiator) where absorbed thermal energy is transferred out of the solution.
Antifreeze is a rather complex mixture of chemical components designed to perform a number of functions in the vehicle including protecting against overheating and freezing, protecting the many dissimilar metals within the cooling system from corrosion, acting as a buffer against acidic contamination, preventing foaming, preventing hard water scaling, reducing the consequences of oil fouling, and protecting diesel wet-sleeve liners from cavitation damage. All of these functions are important and demanding on an engine liquid coolant. Each of the above-mentioned functions must be specifically considered or, at some point, engine damage will occur. To obtain enhanced protection, engine liquid coolants often include a well-balanced additive package that may include up to 15 different inhibitors or more in addition to the commonly known components such as water, ethylene glycol, and dye. Most inhibitors are introduced as sodium or potassium salts and usually are specific in providing corrosion inhibition to one or two metals in the vehicle cooling system.
As antifreeze ages and undergoes hours of use in a vehicle's cooling system, it also accumulates many different types of contaminates. These include oil from leaking oil coolers and water pump lubricants, corrosion products in the form of metal ions and metal hydroxides (i.e., aluminum hydroxide can be produced through aluminum cylinder head corrosion), acids from blow-by gasses, and glycol degradation products such as glycolic, formic, oxalic, acetic acid. Other impurities may be present in the water used to dilute the antifreeze concentrate. These are ions, more commonly known as “minerals”, and may include chlorides, sulfates, carbonates, and metal cations such as calcium and magnesium. Chlorides and sulfates are corrosive and calcium and magnesium cause scaling. In areas with very poor water quality, trace amounts of metals may also be present, especially iron and lead.
Due to the introduction of impurities with extended use of antifreeze in an automotive cooling system, the implementation of certain maintenance procedures is often required for extended coolant usage. The most common procedure is to remove and replace the engine coolant composition after a pre-established time period. In some instances, cooling system additives, which are alkaline and include corrosion inhibitors, are directly added to the coolant to enhance the coolant properties, decrease the corrosive effects, and postpone replacement of the coolant. However, detecting when replacement of the engine coolant or addition of an additive is needed has proven difficult absent the traditionally wasteful method of removing the coolant after a pre-determined period of time.